Posted
by
kdawson
on Friday April 03, 2009 @07:58AM
from the warp-zero-mister-sulu dept.

KentuckyFC writes "Warp drives were generally considered impossible by mainstream scientists until 1994 when the physicist Michael Alcubierre worked out how to build a faster-than-light drive using the principles of general relativity. His thinking was that while relativity prevents faster-than-light travel relative to the fabric of spacetime, it places no restriction on the speed at which regions of spacetime may move relative to each other. So a small bubble of spacetime containing a spacecraft could travel faster than the speed of light, at least in principle. But one unanswered question was what happens to the bubble when quantum mechanics is taken into account. Now, a team of physicists have worked it out, and it's bad news: the bubble becomes unstable at superluminal speeds, making warp drives impossible (probably)."

Well, maybe. Technically because you haven't seen it or work or not work it's both working and not-working at the same time. So, the trick is to keep your eyes closed at all times, and you'll be able to visit strange new worlds, boldly going where no man has gone before. When you open your eyes, you'll find yourself doing that, or simply daydreaming at the office instead of writing that documentation you promised so long ago.

I imagine that a more feasible technique would be applying buttered toast to a cats back and harnessing the power from that to travel the stars. Sadly, my experiments in that area have all resulted in failure, often with the cat scratching me. I have to admit that my neighbours refer to me as "that weirdo from nextdoors" ever since they saw me and I yelled in an ominous voice: "Stand back, I'm doing SCIENCE!" while holding a cat and a piece of buttered toast.

Yet, reality hit him in the end, because I seem to recall he died as a result of sickness that would not have been dangerous had he never been in the accident. More important than the above tongue twister, his quotes were often planned in order to promote what he viewed as the most successful way to regain his ability to walk--thus, he may not have believed the ultimate truth of them, but he did feel that they would effect a means towards his desired end. Strangely enough, his focus on removing bans on cert

Hi. Literature Nazi* to the rescue, here! The improbability drive's figures are always given in terms of "X to 1 against" where X is greater than 1. While you are correct about probabilities, the figure above was an improbability. Also, 0 is not "nigh impossible" - it is the definition of impossible. Easy mistake, I know.

Also, 0 is not "nigh impossible" - it is the definition of impossible.

Not necessarily. It may be that there are an uncountable number of possible outcomes, and each individual outcome has a zero probability, but large sets of them collectively still have positive probability. At least, models exist where this makes sense...

I think you've got a point. All this time we've been trying to invent warp drives. What we really should be doing is inventing Cylons, so that they can in turn invent better propulsion systems than us.

I was part of a proposal to NASA to build a massive (150 meter diameter) GEO based telescope. When you do the math, it works out to be far cheaper and much less fuel to mine the moon for all the raw titanium and fuel you need, manufacture the parts and then robotically assemble them in orbit, than it would to launch from earth all the pre-manufactured component parts.

It doesn't really matter if we cannot travel faster than the speed of light so long as we can live long enough to get there.
Who cares if it takes 50 years to fly to Alpha Centauri if we can engineer ourselves to live for a thousand!

Either that, or we can just figure out how to get really close to the speed of light, and reap the benefits of time dilation to make the journey only last hours from the traveller's point of view.

Sustaining 1G for several years isn't magic. It's just advanced technology.

James Powell, the co-inventor of super-conducting maglev, described a mechanism to build a 1G rocket to travel to the stars. His basic idea was to use Mercury as a solar collector to manufacture a few tons of anti-matter. When you react the anti-matter, you get both power and ejectable mass moving at very high speed. A sci-fi author, Charles Pelligrino, wrote up the idea in the appendix to his book, Flying to Valhalla [amazon.com].

Yeah but you need a massive amount of fuel to accelerate to C and then slow down again. About 40,000 times the size of the shuttle's boosters.

Perhaps this is why, despite our best efforts, no other civilization has contacted us. It's simply too hard to bridge the huuuuge gap between the stars.

Yes, if I was going to build a universe with all sorts of playthings in it, I'd probably separate the experiments with enough spacetime that when the odd experiment blows up it doesn't really affect any others around it.

Not that I think that the universe was actually designed, but if it was, that would be how I would do it.

One of the nice things about the universe is that it's actually pretty hard to hide phenomenon. We, for instance, have been making no attempt to not blatantly broadcast our location and existence - while the sample size is small, do you really think any other civilization is going to have their first thought upon discovering radio waves be "Damn, better be careful about using lest an impossibly distant alien race finds out where we are!"?

No, far more likely is that if there is life out there, it's simply fa

No, it's time dilation and space contraction. If you're traveling at 0.9c relative to earth, your gamma is something like.44. So if you travel one light year, an observer on earth will see you go one light year in about 1.1 years. But from your perspective, you will have traveled only about.44 light years, and it would take something like.48 years. If you travel fast enough, you can reach even distant stars in very short times from your perspective. But you won't get a nice, tidy Galactic Federation, because people on earth will be getting very old very fast. That's the real problem with relativity. It's not that you can't get somewhere fast. Tell me where you want to go and how fast you want to get there, and we can calculate how fast you need to go (relative to the earth) to make it in that time, and it will be less than c.

In other words, we could (in theory) colonize all of the habitable planets in the galaxy in a fairly short time. But the colonies would all basically be cut off from each other. Even sending a radio message to another colony would take prohibitively long. And forget about "rescue" or "supply" ships.

The scariest part about light-hugging spaceships to me (with thanks to Alastair Reynolds) is the impossibility of rescue. If you've got a ship that's able to continuously produce thrust, you fire that thing up, continue to accelerate until the mid way point to your destination, then flip the ship around and decelerate. Yeah, what happens when the drive fails while you're booking along at.95c? It's not like Star Trek where you "drop out of warp" and stay still. There's no "crash landing" there's no fric

It doesn't really matter if we cannot travel faster than the speed of light so long as we can live long enough to get there.

Who cares if it takes 50 years to fly to Alpha Centauri if we can engineer ourselves to live for a thousand!

Ah, but you could travel to the stars without immortality at FTL speeds - at least from the point of view of a ship's occupants - as long as you choose not to go home again. A constant acceleration drive would enable you to cross the galaxy in a few years of ship time, thanks to

Lets say we do that tomorrow. Now you still need to figure out how to keep food and water on that ship for 50 years. Engineer a fuel source that can carry you with strict safety controls to keep the bag of flesh that is you in alive. Oh, while we're at it we'll need a new groundbreaking psychology that can keep 1,000 yo humans sane, especially ones stuck in a smelly spacecraft for 50 years. I wont hold my breath.

From the article... "strongly implies that such a bubble would be unstable." Sounds like proof to me! Right. Just like it was proved impossible for planes to fly. It might indeed - eventually - prove to be impossible, or impossible to do meaningfully / reliably, but it's pretty unlikely we're in a position to make that call at this time. That's why we do research.

THANK YOU. Once upon a time we all knew that the gods made things fall to the ground. Then we knew that things have the falling nature, and the world was flat so things fell "down" no matter where you were. Then we knew that F=MA. Now we know that E=MC^2. What will supersede relativity? (QM is just too wacky, it has been said that if it doesn't confuse you, you don't understand it. I think that means it's a bad model, and we should just abandon particles. But whatever.)

What makes you think that new developments in physics will contradict that E=MC^2?

In short, physics is further and further refined by research, not contradicted, because new theories don't change the empirical evidence that was used to determine old theories, they just explain it better.

Of course, that doesn't mean new theories don't help development of new technologies, so your point stands.

This isn't anything new, it's an old idea being analysed more rigorously with quantum mechanics.

The problem is that in order to have a region of spacetime moving in relation to the outside universe, space has to expand behind it and contract in front, which demands negative and positive gravity in those regions. You need a large negative mass held in place in front of you, and a large positive mass behind. (We'll leave aside the problem that nobody has demonstrated the existence of negative mass, I personally don't believe it could exist precisely because it would enable FTL, but that's seperate to this point.) What you have to achieve is to have the centre of gravitation of the two masses at the centre of the edges of distortion. It means inevitably that half of the negative mass you are using has to stick out of the bubble ahead of you into normal unwarped space, and so that in order to keep generating the field ahead of you, it has to travel faster than light in its local frame. That is strictly not allowed.

(We'll leave aside the problem that nobody has demonstrated the existence of negative mass, I personally don't believe it could exist precisely because it would enable FTL, but that's seperate to this point.)

Faster-than-light travel always causes causality paradoxes [orionsarm.com], so a priori, FTL drives are impossible unless special relativity is wrong. (That's is a bit like saying that perpetual motion machines are impossible unless thermodynamics is wrong.) The proposed mechanism behind the FTL drive doesn't matter -- it'll still cause a time paradox.

Just like we know any proposed perpetual motion machine must have a flaw, any proposed FTL drive must also have a flaw. They belong to the same class of impossible device, and deserve the same degree of consideration.

There have been some papers that even survived peer review on possible resolutions to this. But this is by far the biggest stake in FTL heart. Ironically this is not the biggest problem with the Alcubierre drive. Negative mass energy being one of them.

IIRC Einstein said they GR and SR may be proven wrong, but that the laws of entropy will never be broken (ie entropy is always getting bigger). I would aggree with this. ie FTL is less sci fi than "vacuum energy" or anti inertia drives.

But if I were a betting man, I would bet on light speed as the ultimate speed limit of the universe.

While what you say may be very true, the problem is that we have yet to come up with a more feasible method of reaching distant planets in a reasonable amount of time.

The next closest idea that Science and Science Fiction have come up with is Wormhole/Space Fold travel. And unless you have some safe way of generating more power than a large star in a safe and contained manner, that's going to be even tougher than FTL or Warp Bubble drive.

As has been pointed out, there are many answers to the problem of interstellar travel that don't involve rewriting the physics of the past 150 years.

Medicine may allow us to live indefinitely, making travel to the stars possible by the sheer power of our lifespan.Computers may allow us to upload our consciousness into them, leading to an indefinite lifespan.Medicine may allow us to freeze ourselves and re-thaw when we get to the destination.Space propulsion may allow us to accelerate at 1g for long periods

entropy dictates that that everything loses to heat. This heat is at such a low energy level eventually that it can't cause any increase in energy to anything at all around it. This is how a system winds down, eventually all the energy in the atom will get sapped off this way and then it will start breaking down. Eventually devolving into the quantum soup that makes up the subatomic particles. Eventually, those too will lose energy to the space around them until everything is the same indistinguishable quantum soup.

This is the cold death scenario, and the only thing that can stop it is space itself increasing the density of energy instead of forever decreasing it. It's the expansion of space that continually provides for this loss of energy.

so no, atoms aren't perpetual motion machines. Though, for practical reasons, unless you need the machine to be functioning billions of years from now, you can call it perpetual.

You bring as proof of a scientific statement an article that demonstrate it using an item (ansible) found in SciFi books?

Um, yes. To show how FTL communication causes paradoxes requires an FTL communication device. None exist in reality, and thus a fictional one must be posited. Ansibles already exist in fiction, so the author lifted that just to make use of the word.

Sorry, but we already have faster-than-light communication trough quantum entanglement. The change in state happens instantly, without any delay, no matter what the distance is.

That doesn't work [wikipedia.org]. You can't transmit information faster than light; contrary to popular conception, quantum entanglement does not involve classical information transfer.

If you have one of a pair of dice, and the other is a thousand light-years away, one way to think of entanglement is to imagine that whatever number you roll is the number that shows up on the other die the next time it is rolled. Even if the two dice are linked, you can't control which number shows up, so you can't use the dice to communicate information.

You can only roll the dice once. After that they are no longer entangled.

So Joe carries 1000 particles, which have twins back home, to Joe's Space TV/VCR Repair Center, which is out near Betelgeuse. I want to send him a message: "Pound pastrami, can kraut, six bagels--bring home for Emma."

That doesn't work either because Joe doesn't know if you have rolled the dice or not.

Entangled particles are like dice that are already rolling, and they stop rolling the moment that either particle is observed.

So you and Joe each have a dice that, say, always roll the same number as each other. You look at your dice to cause it to stop rolling, and see that it rolled a 6. Joe can look at his dice too, and will also see a 6, but he doesn't know if he was the one that caused the dice to stop, or whether it was you who stopped it.

Sorry, but we already have faster-than-light communication trough quantum entanglement. The change in state happens instantly, without any delay, no matter what the distance is. Of course in praxis, you would first have to fly a large mass of entangled matter to the other place at sub-light speed. But when it's there, you could communicate at FTL speeds, until the matter is used up.

No we don't, and no you couldn't. I suppose you're thinking of the EPR paradox? Very well. Let us say that I have a set of electrons in equal spin superpositions, and you, at some distant location, have their entangled counterparts. What's the protocol for communication?

Well, if I measure the spin of my electron 0 about the x axis, then in doing so I will also establish the spin of your electron 0 about that axis. The superposition on your electron has vanished without you touching it. Terrific, that's communication, right? I collapse your electrons in sequence, this one on the x axis, this one y, this one x, and so on, a binary code?

Well, no, it doesn't work like that. How can you tell if I've done anything at my end? By making measurements of your electrons? No - because that will collapse the superposition too. Let's say I measure electron 0's spin around the x axis to be positive. Immediately and instantaneously, faster than light across the universe, the superposition on your electron 0 collapses and I know it to be positive about the x axis.

But you don't know that. You might pick the y axis to measure, which is still a superposition. Or you might pick the x axis, and certainly you'll get a +, but you might have got that anyway. You can measure each electron only once - you change its state in doing so - so you can't do a series of tests, build up the statistics and find that on the y axis it's a 50/50 shot but on the x axis it's + every time. That's what you'd need to do in order to determine that I'd chosen the x axis. That's what you'd need in order to communicate faster than light. But since you only ever get one measurement, you get no information about what I did at the other end.

Sorry, but we already have faster-than-light communication trough quantum entanglement. The change in state happens instantly, without any delay, no matter what the distance is.

You're mis-interpreting quantum mechanics and entanglement. The second sentence in that quote is right, but it doesn't imply the first sentence, which is wrong.

When a quantum entanglement collapses, both of the entangled particles will end up in states that are strongly correlated, even if the two particles are very far apart. So yes you could have two entangled particles that are separated from each other, have them collapse, and there would be "instantaneous" correlations between them.

I thought we knew that combining these two theories resulted in answers we know to be nonsense. So the implication is one or both of them are wrong in some way. So I'm a little confused why we should trust results based on the combination of two theories that don't work together.

Granted I'm just a laymen, but does anyone else want to comment about the intersection of these two theories?

First of all it's worth remembering that quantum mechanics and relativity are not 100% incompatible. In fact "relativistic quantum mechanics" has been around for a long time. Quantum theory was greatly advanced when relativistic effects were included.

But you're right that we have good reason to believe that something is wrong with either quantum mechanics or relativity (or both), since they give contradictory predictions in a certain number of extreme cases. (Quantum gravity is not yet solved...)

However we also have ample evidence that quantum mechanics and relativity are incredibly accurate and predictive theories in a vast range of circumstances. We have every reason to believe that the correct "Theory of Everything" will reduce to conventional quantum mechanics and conventional relativity in the appropriate limits. And thus we have every reason to continue using those theories to make predictions all over the place.

Now a warp bubble is one of those extreme situations where the two theories might be expected to give contradictory results, in which case only the hypothetical theory-of-everything would give the correct answers. But it is certainly still useful to ask what our current theories would predict for these extreme situations. It helps us better understand the theories. And, again, we have reasons to believe that many of the things our current theories predict (even in extreme situations) will be right. Absent the theory-of-everything, quantum mechanics + relativity will give us the "best guess" about how such objects would behave

Yeah it is funny hearing people say they have made a "quantum leap" which would mean "the smallest possible discreet leap". I mean even the show with that name wasn't implying huge leaps, so I don't know how it came to mean that in their heads. Or maybe they mean it's an advancement worthy of Scott Bakula?

I actually liked how the last Bond movie, "Quantum of Solace", used the term correctly. Though this probably confused some people. My roommate thought the name was stupid till I told him what "quantum"

I am completely hopeful for the sake of knowledge and experience that we get to into space like in Star Trek. However, I do note a bit of escapism in some of the hopes for a warp drive. I think people are a bit afraid of the idea that this Earth might be the only world humanity will ever live on. The cynic in me suggests that people want this world to be disposable.

We co-evolved with the planet all the way back to when we were microbes. This world is a part of us. Yes, let's try to break past the speed of light, for the sake of science and achievement. Are we existentially okay with our fate as a species being completely contained in this world? I think we can be.

People do not want this world to be disposable, but they want the option to get off this crazy panet, in the hopes that there will be some sanity once you get away from the current cultural stupidity we see from terrorists and those who support terrorism.

There is also the concern that the stupidity of a few may destroy the world, so getting off the planet is also a survival instinct for the species at this point.

The very people who should be aware how little they know compared to what is possible. They come up with these statements, and they forget that for every problem, there IS a solution, even if they can not figure it out themselves.

The question their current "findings" should be asking is "what makes it unstable?". They may not know, but that is the key to solving the problem.

People forget that scientists used to think that it was impossible to break the sound barrier for various reasons. Then they came up with the idea that the speed of light could not be broken. Time has proven again and again that the only thing stopping ANYTHING is not having the knowledge to do it. Not having knowledge does not make something impossible, it just means a CURRENT inability to do something.

People that argue FTL is inevitable, that our theoretical physics must have a tiny flaw that will allow it to happen, don't understand that this isn't about quantum physics or string theory or even relativity. It's about the basic rules that allow us to understand the universe.

Have to disagree there. It is about relativity. Its relativity that says we live in "4 space" with one time like dimension. Its relativity that makes the prediction that FTL travel can result in causality violations. So it can't not be about it.

You don't even need to modify it that much to prevent causality violations with FTL either. If FTL travel *does* have a preferred inertial frame, IIRC then thats enough. A FTL ether if you like. This however may not be interpreted as a "small" change to relativity